JPH08232604A - Erosion preventing device for steam turbine - Google Patents

Abstract

PURPOSE: To effectively prevent the erosion of a moving blade by surely preventing the drain, which flows on an outer peripheral wall surface of a nozzle, from flowing into the back side of the nozzle because of a secondary flow at a nozzle blade part. CONSTITUTION: An erosion preventing device is provided with an outer peripheral wall 1 forming an annular passage, which is enlarged toward the downstream in the direction of a turbine shaft, a plurality of nozzle blades 4, which are arranged at a certain interval along the circumferential direction on the inner surface side of this outer peripheral wall 1, and a moving blade 5, which is arranged on the rear stage side of this nozzle blade 4 and actuated by the wet steam that is supplied to the annular passage. In addition, a water-droplet- flow regulating means is prepared, which restricts the position in the radial direction of a water droplet, which flows from the outer peripheral surface wall 1 along the nozzle blade surface because of the secondary flow and which is blown off a nozzle rear edge 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for preventing erosion of moving blades of a steam turbine operating with wet steam,
In particular, the present invention relates to an erosion preventive device for a steam turbine that prevents a drain flowing through an outer peripheral wall of a flow path from flowing into a nozzle back side by a secondary flow.

[0002]

2. Description of the Related Art In the vicinity of the final stage of a thermal turbine and in most paragraphs of a nuclear turbine using saturated steam, the rotor blades are operated in wet steam containing a large amount of water droplets. For this reason, the water droplets collide with the inlet edge of the moving blade having a high peripheral speed, which causes a problem of erosion. Particularly in recent years, the number of nuclear turbines with high wetness has increased, and the overall capacity of steam turbines has also increased the size of the final stage rotor blades, so that effective measures against the above-mentioned problems are strongly required. Came.

FIG. 15 shows a water drop streamline N on the meridian plane of a steam turbine. As shown in the figure, nozzle vanes 4 are fixed between a nozzle outer ring 2 forming a nozzle outer peripheral wall surface 1 of a vapor flow path and a nozzle inner ring 3 forming a flow path inner peripheral wall. Further, a moving blade 5 is attached behind the nozzle blade 4.

In the flow path of the steam turbine through which the moist steam flows, the minute water droplets generated by the expansion of the moist steam collide with the nozzle blade 4 and the moving blades 5 and 12 in the upstream and downstream stages thereof, and collect into large water droplets. Will become. The water droplets that collide with the moving blade 12 at the upstream stage of the nozzle blade 4 are shaken off by the moving blade 12 and collide with the nozzle outer peripheral wall surface 1 and become a drain flow on the nozzle outer peripheral wall surface 1. That is, the drain flow in the nozzle portion is roughly divided into two, a drain flow flowing on the surface of the nozzle blade 4 and a drain flow flowing on the nozzle outer peripheral wall surface 1.
Become one

FIG. 16 shows how water droplets are generated on the surface of the nozzle blade. As shown in the figure, the water droplet flow f indicated by the broken line arrow and the vapor flow e indicated by the solid line arrow form the nozzle blade 4
However, the water droplet flow f cannot be diverted due to inertial force and collides with the nozzle belly surface 9 and is collected there.

When the diameter of the water droplet becomes very large, the relative speeds of the water droplet flow and the steam flow at the outlet at the preceding rotor blade are greatly different. Therefore, the water drop flow is different from the steam flow as shown by the broken line arrow g in FIG. It flows in at different angles, collides with the back surface 7 of the nozzle,
It is collected there. In this way, the water droplets collected on the nozzle belly surface 9 and the nozzle back surface 7 are separated by the nozzle blade trailing edge 11
Coarse water droplets are torn from it and collide with the moving blade 5 in the subsequent stage to erode it.

Further, in a steam turbine operating in a wet region, the blade length becomes long, and the centrifugal force, the Coriolis force, and the steam force predominantly move in the outer peripheral direction in the moving blade, and water droplets form the outer peripheral wall surface 1 of the nozzle. And it will adhere to the vicinity of the outer peripheral portion of the nozzle blade 4.

17 and 18 show the pressure distribution on the blade surface of the nozzle blade 4 and the flow in the vicinity of the nozzle outer peripheral wall surface 1, respectively.

As shown in FIG. 17, the surface pressure of the nozzle vanes 4 is high on the nozzle belly surface 9 and low on the nozzle back surface 7. Therefore, in the steam passage portion between the nozzle blades 4, as shown in FIG. 18, a force F from the nozzle belly surface 9 to the nozzle back surface 7 is generated. In particular, on the nozzle outer peripheral wall surface 1, since the flow velocity in the main steam flow direction becomes slow due to the viscosity of the steam, the influence of the force F from the nozzle belly surface 9 to the nozzle back surface 7 becomes large. Therefore, on the outer peripheral wall surface 1 of the nozzle, a vortex flow V, which is a so-called secondary flow, is generated by the force F from the nozzle belly surface 9 to the nozzle back surface 7.

FIG. 19 shows a water drop streamline N that propagates along the nozzle outer peripheral wall surface 1, and FIG. 20 shows the water drop streamline N near the nozzle outer peripheral wall surface 3 in three dimensions. As shown in FIG. 19, a large amount of drain flows into the nozzle back surface 7, and the nozzle back surface 7
20, the drain reaches the nozzle blade trailing edge 11 while moving to the nozzle inner ring 1 side on the nozzle back face 7 due to the influence of the secondary flow, and is torn as a coarse water droplet and is torn in the latter stage. Collides with the blade and erodes it.

In order to prevent such erosion, a device for removing water droplets in a steam turbine has been conventionally proposed (for example, Japanese Patent Publication No. 49-9522). 21 and 2
2 shows the configuration of the water droplet removal device according to this proposal. 21 is a cross-sectional view of the nozzle blade on the meridian plane.
2 is a sectional view taken along line JJ of FIG.

In this apparatus, the nozzle vane 4, the nozzle outer ring 2 which holds the nozzle vane 4, and the nozzle inner ring 3 are all hollow, and the hollow portions 18, 19, 20 communicate with each other. ing. Then, slit-shaped water droplet suction ports 8 and 6 are formed in the nozzle belly surface 9 and the nozzle back surface 7 along the radial direction, respectively, and the nozzle belly surface 9 of one nozzle blade 4 adjacent to each other also on the nozzle outer peripheral wall surface 1. A slit-shaped water droplet suction port 10 is provided between the nozzle back surface 7 and the nozzle back surface 7 of the other nozzle blade 4.

The hollow portion 19 on the nozzle outer ring 2 side communicates with a low-pressure source such as a condenser (not shown), and the water droplet suction port 6,
Water droplets are sucked from 8 and 10.
The water droplets that have propagated through the nozzle belly surface 9 are from the water droplet suction port 8 of the nozzle belly surface 9 and those that have traveled through the nozzle back surface 7.
From the water droplet suction port 6 on the nozzle back surface 7, each is sucked into the hollow portion 18, and further flows into the condenser from the hollow portion 19 on the nozzle outer ring 2 side. Further, the water droplets that have propagated through the nozzle outer peripheral wall surface 1 are sucked into the hollow portion 19 from the water droplet suction port 10 of the nozzle outer peripheral wall surface 1, and this also flows into the condenser.

FIG. 23 shows a nozzle blade 4 having a water droplet suction port.
3 shows the positional relationship between the water droplet suction ports 6 and 8.
Since the water droplets are sucked into the same hollow portion 18 through these water droplet suction ports 6 and 8, as shown in FIG. 23, the nozzle belly surface 9 and the nozzle back surface 7 are bored at positions where the pressures are equal to each other. To be done.

On the other hand, on the outer peripheral wall surface 1 of the nozzle, the drain is sucked through the water droplet suction port 10 described above. Since the pressure in the hollow portion 19 of the nozzle outer ring 2 on the suction side is almost equal to the pressure in the hollow portion 18 of the nozzle vane 4, the water droplet suction port 10 of the nozzle outer ring 2 has a nozzle belly surface 9 and a nozzle belly surface 9 as shown in FIG. It is provided on a straight line connecting the water droplet suction ports 6 and 8 on the back surface 7 of the nozzle.

FIG. 24 shows another proposal (JP-A-4-2462).
No. 05) shows the configuration of the erosion reducing device. According to this other proposal, as shown in FIG. 24, a water barrier 23 having a slight height is installed on the nozzle back surface 7 of the nozzle blade 4, so that the secondary flow flows from the outer peripheral wall surface 1 to the nozzle back surface 7. The drain can be stopped. The dammed drain is guided to the feed water reheater by using a water collecting device (not shown).

In this way, the water droplets propagating along the surfaces of the nozzle blade 4 and the nozzle outer ring 2 are removed, and the generation of coarse water droplets on the nozzle trailing edge blade 11 is reduced, thereby reducing the erosion of the moving blade. It is like this.

[0018]

However, actually, even if the above-mentioned conventional water drop removing device is adopted, it is not always possible to sufficiently remove the water drops, and erosion of the moving blade occurs. The reason will be described in detail below.

In order to reliably prevent the erosion of the moving blade due to the coarse water droplets torn from the trailing edge 11 of the nozzle blade, all the drain on the surface of the nozzle blade 4 must be captured. In that case, it is necessary to capture the drain flowing on the surface of the nozzle blade 4 toward the nozzle trailing edge 11 as much as possible downstream of the surface of the nozzle blade 4.

In particular, since the drain flowing on the nozzle outer peripheral wall surface 1 flows into the nozzle back surface 7 under the influence of the secondary flow, it is ideal that the water droplet suction ports 6 and 8 are as close to the nozzle blade trailing edge 11 side as possible. However, in general, as described above, since the water droplet suction port 6 on the nozzle back surface 7 and the water droplet suction port 8 on the nozzle belly surface 9 are arranged at positions where the pressure is equal on the blade surface, the nozzle belly surface 9 The water droplet suction port 8 is formed on the nozzle rear edge side, and the water droplet suction port 6 on the nozzle back surface 7 is formed on the nozzle front edge side.

Further, in order to capture all the drainage flowing on the surface of the nozzle blade 4 and the outer peripheral wall surface 1 of the nozzle, the water droplet suction port 10 of the outer peripheral wall surface 1 of the nozzle is connected to the water droplet suction ports 6, 8 on the surface of the nozzle blade 4. Need to let. However, there is a problem in strength in communicating the water droplet suction port 10 of the outer peripheral wall surface 1 of the nozzle with the water droplet suction ports 6 and 8 on the nozzle surface.

25 and 26 show the above-mentioned Japanese Patent Publication No.
The water drop streamline N when the water drop inlets 6, 8 and 10 of No. 9-9522 are provided is shown.

As shown in these figures, the water drop suction port 6,
The drain M flowing in the area not covered by 8 and 10 is not removed but is removed by the above-mentioned secondary flow to the nozzle rear surface 7
And reaches the trailing edge 11 of the nozzle blade and is blown off by steam force to form coarse water droplets, which erode the moving blade.

Further, a water barrier 23 having a slight height is installed on the back surface 7 of the nozzle of the above-mentioned JP-A-4-246205,
According to the result of the model test, it is clear that the technique of preventing the drain from flowing into the nozzle back surface 7 by the secondary flow cannot prevent the drain from flowing toward the nozzle inner ring 3 side with the water barrier having a slight height. became. The reason for this is that the vortex diameter of the secondary flow develops greatly near the trailing edge of the nozzle back surface 7, so the drain rides over the water barrier 23, and the drain that rides over this water barrier 23 becomes coarse water droplets as it is and after the nozzle blade. This is because it is blown off from the edge 11.

The present invention has been made in view of such various circumstances, and an object thereof is to reliably prevent the drain flowing on the outer peripheral wall surface of the nozzle from flowing into the back side of the nozzle by the secondary flow in the nozzle blade portion. However, it is another object of the present invention to provide an erosion prevention device for a steam turbine that can effectively prevent erosion of a moving blade.

[0026]

In order to achieve the above object, the invention according to claim 1 defines an outer peripheral wall forming an annular flow passage that expands toward the turbine axial direction downstream side, and an inner surface of the outer peripheral wall. Turbine equipped with a plurality of nozzle blades arranged at intervals along the circumferential direction on the side, and a moving blade arranged on the rear side of the nozzle blades and operated by the wet steam supplied to the annular flow path. In the above, a water drop flow restricting means is provided for restricting a radial position of a water drop that is transmitted from the outer peripheral wall on the nozzle blade surface by the secondary flow and is blown off from the nozzle trailing edge.

According to a second aspect of the present invention, in the erosion prevention device for a steam turbine according to the first aspect, the nozzle blades are convex toward the ventral surface of the nozzle with respect to a reference radial line passing through the rotation center of the turbine rotor, as water droplet flow restricting means. It is characterized in that it is curved or inclined in the circumferential direction to have a shape.

According to a third aspect of the present invention, in the erosion preventive device for a steam turbine according to the first aspect, the water droplet flow restricting means is an annular partition plate which is attached to the entire circumference in parallel with the outer peripheral wall surface of the nozzle. Erosion prevention device for steam turbines.

According to a fourth aspect of the invention, in the steam turbine erosion prevention device according to the third aspect, the outflow angle of the nozzle blade is α, the axial distance from the nozzle blade trailing edge to the blade leading edge is A, and the moving blade is When the radius is B, the radial position R at the trailing edge of the nozzle blade at the end of the partition plate is

[Equation 2] It is characterized by setting so that

The invention according to claim 5 is the invention according to claim 3 or 4.
In the erosion prevention device of the steam turbine described,
Two or more nozzle blades, partition plates provided on these nozzle blades and nozzle inner and outer rings are integrally manufactured by precision casting, and these nozzle blades, partition plates and nozzle inner and outer rings are joined in the circumferential direction, and It is characterized in that the partition plates are connected to each other at both the ventral side surface and the dorsal side surface of the nozzle blade to form a turbine nozzle.

According to a sixth aspect of the present invention, in the erosion preventive device for a steam turbine according to the first aspect, a hole penetrating the ventral side surface and the back side surface of the nozzle blade is bored as the water drop flow restricting means. The opening of the hole on the back side of the nozzle blade is directed toward the outer peripheral side of the nozzle blade.

[0032]

According to the present invention, by controlling the radial position of the water droplets blown off from the trailing edge of the nozzle blade by the water droplet flow regulating means, the drain flowing from the outer peripheral wall to the nozzle back side by the secondary flow can be prevented. It can be kept in the vicinity, and by causing the drain blown off from the trailing edge of the nozzle blade to collide with the outer peripheral wall of the nozzle before reaching the moving blade, erosion of the moving blade due to collision of water droplets can be prevented.

In this case, the nozzle blade is curved or inclined in the circumferential direction so as to be convex toward the nozzle belly surface with respect to the reference radial line passing through the center of rotation of the turbine rotor, so that the secondary flow causes the nozzle blade to move from the outer peripheral wall to the nozzle blade. The erosion of the moving blade can be reduced by effectively pressing the drain flowing into the back surface of the nozzle to the vicinity of the outer peripheral wall by the fluid force and increasing the position of the water droplets blown off from the trailing edge of the nozzle blade in the radial direction.

Further, the drain that flows from the outer peripheral wall to the back surface of the nozzle due to the secondary flow is blocked by the partition plate, and the position of the water droplets blown off from the trailing edge of the nozzle is increased in the radial direction to reduce the erosion of the moving blade. it can.

Further, due to the pressure difference between the ventral side surface and the back side surface of the nozzle blade, the drain flowing on the back side surface is moved to the vicinity of the outer peripheral wall, and the fluid force blown toward the outer peripheral wall at the back side surface causes the outer peripheral wall to move to the nozzle rear surface. The erosion of the moving blade can be reduced by pressing the drain flowing into the outer peripheral wall surface to increase the radial position of the water droplets blown off from the rear end of the nozzle.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a steam turbine erosion prevention device according to the present invention will be described below with reference to the drawings. Note that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals.

First Embodiment (FIGS. 1 to 3) FIGS. 1 and 2 show the structure of an erosion prevention device for a steam turbine according to this embodiment. As shown in FIGS. 1 and 2, a nozzle outer ring 2 forming a nozzle outer peripheral wall surface 1 of a vapor flow path and a nozzle inner ring 3 forming a flow path inner peripheral wall 3
The nozzle blades 4 are fixed between and. Further, a moving blade 5 is attached behind the nozzle blade 4.

A nozzle back surface suction port 6 is formed on the nozzle back surface 7, a nozzle belly surface suction port 8 is formed on the nozzle blade belly surface 9, and a nozzle outer peripheral wall suction port 10 is formed on the nozzle outer peripheral wall surface 1.
It is designed to absorb water drops.

As shown in FIG. 2, with respect to the reference radial line G passing through the center of rotation 13 of the turbine rotor, the nozzle blades 4 are curved in the circumferential direction so as to be convex in the nozzle belly direction. A water drop flow control means is configured.

Next, the operation of this embodiment having the above construction will be described with reference to FIG. FIG. 3 is a diagram showing the nozzle outflow direction in three dimensions.

As shown in the figure, a throat 21 as a minimum passage is provided in the flow path through which the fluid passes between the nozzle blades 4, and the fluid flows out in a direction orthogonal to the throat 21. .

When the throats 21 are stacked in the radial direction, a throat surface 22 is formed. When considered three-dimensionally, the fluid flows out in a direction orthogonal to the throat surface 22. Therefore, since the drainage flowing on the nozzle blade back surface 7 is pressed against the nozzle outer peripheral wall surface 1 side by the secondary flow due to the fluid force, the radial position of the water droplets blown off from the nozzle trailing edge 11 as in the present embodiment. By increasing, the water droplet flow can be restricted to the tip end side of the moving blade 5 on the rear stage side, and erosion of the moving blade 5 can be prevented.

Further, according to the present embodiment, even when the water droplet suction port 10 on the outer peripheral wall surface 1 of the nozzle is not provided, the outer peripheral wall surface 1 of the nozzle is
All the drains flowing above are blown to the outside of the tip turning radius of the moving blade 5, and can be completely removed by the conventionally provided drain catcher. Therefore, the nozzle outer peripheral wall surface suction port 10 may be omitted.

Second Embodiment (FIGS. 4 and 5) FIG. 4 shows the structure of a second embodiment of the erosion prevention device for a steam turbine according to the present invention. The same parts as those in the first embodiment will be described with the same reference numerals.

The difference from the first embodiment is that the nozzle blade 4
With respect to the reference radial line G passing through the center of rotation of the turbine rotor, is inclined in the circumferential direction so as to be convex in the nozzle belly direction.

According to this embodiment having such a configuration, as shown in FIG.
As shown in FIG. 7, as in the first embodiment, the drain flowing through the nozzle back surface 7 is pressed against the nozzle outer peripheral wall side by the secondary flow to increase the radial position of the water droplets blown off from the nozzle trailing edge. The moving blade 5
The erosion of can be prevented.

Third Embodiment (FIGS. 6 to 8) FIGS. 6 and 7 show the construction of a third embodiment of the erosion prevention device for a steam turbine according to the present invention. In addition,
The same parts as those of the first embodiment are designated by the same reference numerals and described.

As shown in FIGS. 6 and 7, in this embodiment, an annular partition plate 14 is attached over the entire circumference in parallel with the nozzle outer peripheral wall surface 1.

In this embodiment, as shown in FIG.
The entire nozzle is formed by processing a nozzle composed of two or more nozzle blades 4, nozzle inner and outer rings 2, 3 and partition plate 14 by a precision casting method, and combining a plurality of them into an annular shape. At the time of manufacturing, as shown in FIG. 7, each partition plate 14 is processed so that the tips thereof protrude by a half pitch, and these are joined later.

Next, the operation of this embodiment having the above structure will be described.

As described above, even if the water barrier 17 having a slight height is installed on the nozzle back surface 7, it is not possible to prevent the drain from flowing into the nozzle back surface 7 from the nozzle outer peripheral wall surface 1 by the secondary flow. Therefore, in order to completely stop it, it is necessary to attach the annular partition plate 14 to the entire circumference.

In FIG. 6, an annular partition plate 14 is attached to the entire circumference in parallel with the outer peripheral wall surface 1 of the nozzle,
It is possible to prevent the drainage flowing on the back surface 7 of the nozzle and to fly the drain to the outside of the tip turning radius of the moving blade 5 to prevent the erosion of the moving blade 5.

Of course, water droplets blown off from the previous stage also adhere to the partition plate 14 on the inner surface 15 of the partition plate 14, but since it is overwhelmingly smaller than the amount of drain flowing on the outer peripheral wall surface 1,
It has almost no effect on the erosion of the moving blade 5.

Further, according to the model test, the drain on the outer peripheral wall surface 1 of the nozzle is the axial chord length C of the end portion on the outer peripheral side of the nozzle blade.
Since it flows into the nozzle back surface 7 on the downstream side from 1/2 of the above, if the partition plate 14 is from C / 2 to the nozzle blade trailing edge 11, the moving blade 5 due to the secondary flow on the inner surface 15 of the partition plate 14
Most erosion can be prevented.

On the other hand, the specific gravity of the water droplet is sufficiently larger than that of the steam of the main stream, and it is blown off from the nozzle trailing edge 11 at a right angle to the nozzle trailing edge line without being affected by the fluid force of the main stream.

FIG. 8 shows the trajectory of water droplets blown off from the trailing edge 11 of the nozzle. In this figure, the nozzle outflow angle is α, the axial distance from the nozzle tip trailing edge to the blade tip front edge is A, and the blade tip rotation radius B is.
Further, when the drain blown off from the nozzle trailing edge 11 hits the blade tip front edge, the radial distance of the nozzle trailing edge position 16 of the drain is R, and the collision position where the drain hits the blade tip front edge is D.

With the geometrical shape shown in this figure,

(Equation 3) Then, the drain collides with the outer peripheral wall before reaching the leading edge of the blade tip. Therefore,

[Equation 4] In the case of, the drain does not hit the moving blade 5 and erosion can be prevented.

Fourth Embodiment (FIGS. 9 to 11) FIG. 9 shows the structure of a fourth embodiment of the erosion prevention device for a steam turbine according to the present invention. The same parts as those in the first embodiment will be described with the same reference numerals.

In FIG. 9, in the present embodiment, a plurality of holes 17 penetrating the vicinity of the outer peripheral wall of the nozzle belly surface 9 and the nozzle back surface 7 of the nozzle blade 4 are formed, and the opening of the hole 17 on the back side of the nozzle is the nozzle. It is directed toward the blade outer peripheral wall surface 1. Further, the radial positions of the holes 17 penetrating the nozzle belly surface 9 and the nozzle back surface 7 are set to be equal.

Next, the operation of this embodiment having the above structure will be described.

FIG. 10 is a pressure distribution chart of the nozzle surface, where the horizontal axis represents the axial position of the nozzle blade and the vertical axis represents the pressure.
Each is made dimensionless by using the axial distance of the nozzle blade and the total pressure at the nozzle blade inlet. Since the pressure b on the nozzle back side is lower than the pressure a on the nozzle antinode side, the fluid flows from the nozzle antinode side to the hole 17
To the nozzle back side via.

FIG. 11 shows the shape of the opening of the hole 17 on the back side of the nozzle. As shown in FIG. 11, by directing the holes 17 that are open to the back of the nozzle blade toward the outer peripheral wall surface 1 of the nozzle blade, the fluid passing through the holes 17 blows out toward the outer peripheral wall surface 1, so that the secondary flow Nozzle back surface 7
The drain flowing through can be pressed against the outer peripheral wall surface 1.

Therefore, the drainage flowing on the nozzle back surface 7 due to the secondary flow is pressed to the nozzle outer peripheral wall side by the fluid force, and the position of the water droplets blown off from the nozzle trailing edge is increased in the radial direction, so that the erosion of the moving blade 5 is increased. Can be prevented.

Fifth Embodiment (FIGS. 12 to 14) FIG. 12 shows the structure of a fifth embodiment of the steam turbine erosion prevention device according to the present invention. The first
The same parts as those in the embodiment will be described with the same reference numerals.

As shown in FIG. 12, in this embodiment, a hole 18 penetrating the nozzle belly surface 9 of the nozzle blade 4 and the outer peripheral wall of the nozzle back surface 7 is bored, and the opening of the hole 17 on the back side of the nozzle is formed. It is directed toward the outer peripheral wall surface 1 of the nozzle blade. further,
The radial position of the opening of the nozzle belly surface 9 is set smaller than the radial position of the opening of the nozzle back surface 7.

Next, the operation of this embodiment having the above structure will be described.

FIG. 13 is a pressure distribution diagram on the nozzle surface, which is dimensionless like the fourth embodiment. Hole 17
Since the pressure b at the nozzle back side opening is lower than the pressure c at the nozzle back side opening, the fluid moves from the nozzle back side to the nozzle back side through the hole 17.

FIG. 14 shows the shape of the opening of the hole 17 on the back side of the nozzle. As shown in FIG. 14, by directing the holes 17 opened on the back side of the nozzle blade toward the outer peripheral wall surface 1 of the nozzle blade, the fluid passing through the holes 17 is blown out toward the outer peripheral wall surface 1, so that the secondary flow is generated. The drain flowing through the nozzle back surface 7 can be pressed against the outer peripheral wall surface 1.

Therefore, the drain flowing on the nozzle back surface 7 by the secondary flow is pressed against the outer peripheral wall side of the nozzle by the fluid force, and the position of the water droplets blown off from the trailing edge of the nozzle is increased in the radial direction, so that the moving blade 5 moves. Erosion can be prevented.

[0070]

As described above in detail, according to the present invention, the secondary flow allows the drain flowing from the outer peripheral wall to the back side of the nozzle to be kept near the outer peripheral wall and blown off from the trailing edge of the nozzle blade. Since the drains collide with the outer peripheral wall of the nozzle before reaching the moving blade, it is possible to prevent erosion of the moving blade due to collision of water droplets.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a turbine configuration in a first embodiment of an erosion prevention device for a steam turbine according to the present invention.

FIG. 2 is a view of the nozzle blade shown in FIG.

FIG. 3 is an explanatory view showing a fluid outflow direction in the embodiment.

FIG. 4 is a view of a nozzle blade in a second embodiment of an erosion preventive device for a steam turbine according to the present invention, viewed from the nozzle outlet direction.

FIG. 5 is an explanatory view showing the outflow direction of the fluid in the embodiment.

FIG. 6 is a cross-sectional view showing a turbine configuration in a third embodiment of the steam turbine erosion prevention device according to the present invention.

FIG. 7 is an explanatory view showing a method of assembling the nozzle in the embodiment.

FIG. 8 is an explanatory diagram showing a moving distance of the drain blown off from the trailing edge of the nozzle in the embodiment.

FIG. 9 is a cross-sectional view showing a turbine configuration in a fourth embodiment of an erosion prevention device for a steam turbine according to the present invention.

FIG. 10 is a view showing blade surface pressure at the same radial height in the example.

FIG. 11 is a diagram showing an opening position of a hole on the back side of a nozzle in the embodiment.

FIG. 12 is a cross-sectional view showing a turbine configuration of a steam turbine erosion prevention device according to a fifth embodiment of the present invention.

FIG. 13 is a view showing blade surface pressures at different radial positions in the example.

FIG. 14 is a view showing an opening position of a hole on the back side of a nozzle in the embodiment.

FIG. 15 is a cross-sectional view showing a water droplet streamline at a paragraph in a steam turbine.

FIG. 16 is an explanatory diagram showing a generation state of water droplets on the surface of a nozzle blade.

FIG. 17 is a pressure distribution diagram of the nozzle blade surface.

FIG. 18 is an explanatory diagram showing a vortex flow near the outer peripheral wall of the nozzle.

FIG. 19 is a water droplet streamline diagram on the outer peripheral wall surface of the nozzle.

FIG. 20 is a water drop stream diagram in the vicinity of the outer peripheral wall of the nozzle.

FIG. 21 is a nozzle cross-sectional view showing a conventional erosion prevention device.

22 is a cross-sectional view taken along the line JJ of the outer peripheral wall surface shown in FIG.

23 is an explanatory view showing the position of a water droplet suction port on the surface of the nozzle blade shown in FIG. 21.

FIG. 24 is an explanatory view showing another conventional example and showing a nozzle blade and a water barrier.

FIG. 25 is a waterdrop streamline diagram on the outer peripheral wall surface when the outer peripheral wall surface is provided with a water droplet inlet.

FIG. 26 is a water droplet streamline diagram in the vicinity of the outer peripheral wall when water droplet suction ports are provided on the outer peripheral wall surface and on the nozzle back side, respectively.

[Explanation of symbols]

 1 Nozzle Outer Wall Surface 2 Nozzle Outer Ring 3 Nozzle Inner Ring 4 Nozzle Blade 5 Moving Blade 6 Nozzle Back Suction Port 7 Nozzle Back Surface 8 Nozzle Vent Face Suction Port 9 Nozzle Vent Face 10 Nozzle Outer Wall Suction Port 11 Nozzle Trailing Edge 12 Moving Blade 13 Rotation Center Line 14 Partition plate 15 Partition plate inner surface 16 Partition plate nozzle trailing edge radial position 17 Hole penetrating the nozzle back surface 18 Nozzle blade hollow part 19 Nozzle outer ring hollow part 20 Nozzle inner ring hollow part 21 Throat 22 Throat surface 23 Water barrier surface A After partition plate nozzle Distance from edge point to blade tip front edge B Blade tip radius C Axial chord length of nozzle outer edge D Collision position of water droplet F Force from nozzle vent face to back face G Standard radial line H At nozzle trailing edge Droplet radius M, N Droplet streamline R Nozzle trailing edge radius of partition V Vortex flow α Nozzle outflow angle a Nozzle ventral side wall b near the nozzle dorsal peripheral wall pressure c any nozzle ventral pressure d any nozzle back side pressure e vapor streamlines f, g water droplets streamlines

Claims (6)

[Claims] 1. An outer peripheral wall forming an annular flow path that expands toward the downstream side in the turbine axial direction, and a plurality of nozzle blades arranged on the inner surface side of the outer peripheral wall at intervals along the circumferential direction,
In a steam turbine equipped with a moving blade that is arranged on the subsequent stage side of this nozzle blade and that is operated by the wet steam supplied to the annular flow path, the secondary flow propagates from the outer peripheral wall onto the nozzle blade surface, and the nozzle trailing edge An erosion preventive device for a steam turbine, comprising: a water drop flow restricting means for restricting a radial position of a water drop blown off from the steam turbine. 2. The erosion preventive device for a steam turbine according to claim 1, wherein, as the water drop flow restricting means, the nozzle blade is formed into a convex shape in the nozzle abdominal direction with respect to a reference radial line passing through the rotation center of the turbine rotor. An erosion preventive device for a steam turbine, which is curved or inclined in a direction. 3. The steam turbine erosion prevention device according to claim 1, wherein the water droplet flow restricting means is an annular partition plate which is attached to the entire circumference in parallel with the outer peripheral wall surface of the nozzle. Erosion prevention device. 4. The steam turbine erosion prevention device according to claim 3, wherein the outflow angle of the nozzle blade is α, the axial distance from the nozzle blade trailing edge to the blade leading edge is A, and the blade radius is B. At this time, the radial position R at the trailing edge of the nozzle blade at the partition plate end is given by An erosion preventive device for a steam turbine, characterized by being set as follows. 5. The steam turbine erosion prevention device according to claim 3, wherein two or more nozzle blades are provided.
The partition plate and the nozzle inner and outer rings provided on these nozzle blades are integrally manufactured by precision casting, and the nozzle blade, the partition plate and the nozzle inner and outer rings are joined in the circumferential direction, and the partition plates are the nozzle blades. An erosion preventive device for a steam turbine, characterized in that it is connected to both the ventral side surface and the back side surface by a protruding portion to form a turbine nozzle. 6. The erosion prevention device for a steam turbine according to claim 1, wherein a hole penetrating a ventral side surface and a back side surface of the nozzle blade is bored as the water drop flow restricting means, and the penetrating surface of the nozzle blade backside surface. An erosion preventive device for a steam turbine, characterized in that an opening portion of the steam turbine is directed toward an outer peripheral side of a nozzle blade.